1. Field of the Invention
The present invention relates to surface acoustic wave branching filters for use as branching filters that are connected to, for example, antenna portions of wireless communication apparatuses. More specifically, the present invention relates to a surface acoustic wave branching filter having a structure in which first and second surface acoustic wave filter chips having different center frequencies are joined via bumps provided on the surface acoustic wave filter chips, to a wiring pattern provided on a packaging member.
2. Description of the Related Art
In recent years in order to achieve further miniaturization, various branching filters using surface acoustic wave filters have been under development for use in compact wireless communications apparatuses, such as portable telephones.
In this type of surface acoustic wave filter branching filter, first and second surface acoustic wave filters having different center frequencies are mounted in a package. There is a strong demand for more secured isolation between the first and second surface acoustic wave filters.
One example of structures for improving the isolation is disclosed in Japanese Unexamined Patent Application Publication No. 5-167389 (Patent Document 1). Thus, as shown in FIG. 19, in a surface acoustic wave branching filter 201 described in Patent Document 1, first and second surface acoustic wave filter chips 203 and 204 are mounted in a packaging member 202. The packaging member 202 has signal input/output terminals C1, C2, D1, and D2. The first surface acoustic wave filter chip 203 has signal input/output terminals A1 and A2, and the second surface acoustic wave filter chip 204 has signal input/output terminals B1 and B2. The signal input/output terminals A1, A2, B1, B2, C1, C2, D1, and D2 are arranged such that a signal line connecting the signal input/output terminals A1, A2, and C2 and a signal line connecting the signal input/output terminals B1, B2, and D2 are arranged along two straight lines (X, Y) that cross each other at substantially right angles. With such an arrangement of the signal input/output terminals, inductive coupling is suppressed between the plurality of signal lines and the isolation is improved.
Meanwhile, Japanese Unexamined Patent Application Publication No. 8-18393 (Patent Document 2) teaches a branching-filter package shown in FIG. 20. In this case, first and second surface acoustic wave filter chips 212 and 213 are accommodated in a branching-filter package 211 having a multilayer structure. Striplines 214 and 215 are embedded in the branching-filter package 211 to constitute phase matching circuits. The characteristic impedances of the striplines 214 and 215 are greater than the characteristic impedance of an external circuit that is connected to the branching-filter package. In addition, at least two ground terminals are provided in the package for one surface acoustic wave filter chip, thereby improving the attenuation.
In a surface acoustic wave branching filter disclosed in Japanese Unexamined Patent Application Publication No. 2003-51731 (Patent Document 3), surface acoustic wave chips that constitute first and second surface acoustic wave filters are accommodated in a package. In this case, the first and second surface acoustic wave filters are electrically connected to terminal electrodes arranged in the package using bonding wires. In this surface acoustic wave branching filter, a bonding wire that is connected to a signal terminal and a bonding wire that is connected to a ground terminal cross each other in the first surface acoustic wave filter, thereby improving the isolation and attenuation.
In the configuration described in Patent Document 1, the signal lines of the first and second surface acoustic wave filter chips are arranged in a manner described above to suppress mutual inductive coupling therebetween. However, with this arrangement, although the mutual inductance can be suppressed to some extent, the suppression is still not enough. Thus, with the surface acoustic wave branching filter 201, the isolation between the first and second surface acoustic wave filter chips is not sufficient.
Additionally, when a mounting displacement between the first and second surface acoustic wave filter chips occurs, there is a problem in that the attenuation and isolation characteristics deteriorate to a great extent.
Meanwhile, for the configuration described in Patent Document 2, when it is applied to a flip-chip-bonding system packaging structure having low inductance components, the attenuation cannot be sufficiently improved because of its low inductance components.
The surface acoustic wave branching filter described in Patent Document 3 achieves cancellation of current due to mutual inductance, by crossing the bonding wires. This structure, however, makes it difficult to achieve miniaturization of a surface acoustic wave branching filter because of the use of bonding wires.
In order to overcome the problems described above, preferred embodiments of the present invention provide a surface acoustic wave branching filter that has first and second surface acoustic wave filter chips mounted with bumps in a packaging member by a flip-chip bonding system, that allows miniaturization, that further improves isolation between the surface acoustic wave filter chips, that achieves a favorable attenuation characteristic, and that has small characteristic variations due to mounting displacement of the surface acoustic wave filter chips.
According to a first preferred embodiment of the present invention, a surface acoustic wave branching filter includes a first surface acoustic wave filter chip having a relatively low center frequency and a second surface acoustic wave filter chip having a relatively high center frequency which are joined using a plurality of bumps provided on the first and second surface acoustic wave filter chips to wiring patterns disposed on a chip-mounting surface of a packaging member. The surface acoustic wave branching filter includes a first surface acoustic wave filter chip that includes a plurality of SAW resonators and that has a plurality of bumps on the lower surface, a second surface acoustic wave filter chip that includes a plurality of SAW resonators and that has a plurality of bumps on the lower surface, and a packaging member to which the first and second surface acoustic wave filter chips are joined using the plurality of bumps. The chip mounting surface of the packaging member has, at least, a signal wiring pattern that is connected to an output end of the second surface acoustic wave filter chip and a ground wiring pattern that is connected to a ground potential of a SAW resonator that is in closest proximity to the output end of the second surface acoustic wave filter chip. The chip mounting surface has a signal via hole electrode and a ground via hole electrode which are connected to the signal wiring pattern and the ground wiring pattern, respectively, and which penetrate at least one portion of the packaging member. The signal wiring pattern is configured to have a pattern portion that is in closer proximity to the ground wiring pattern than to the bump, joined to the signal wiring pattern, of the second surface acoustic wave filter chip.
In the first preferred embodiment of the present invention, the signal wiring pattern is bent so as to be in close proximity to the ground wiring pattern. Thereby, the signal wiring pattern has a pattern portion that is in close proximity to the ground electrode pattern.
In the first preferred embodiment of the present invention, the signal wiring pattern has first, second, and third wiring pattern portions. The first wiring pattern portion extends substantially parallel to an edge of the ground wiring pattern at a portion in close proximity to the ground wiring pattern. The second and third wiring pattern portions are bent from two opposite ends of the first wiring pattern portion in a direction spaced away from the ground wiring pattern.
In the first preferred embodiment of the present invention, the first wiring pattern portion and the second and third wiring pattern portions are arranged to form substantially right angles, so that the signal wiring pattern has a substantially U shape.
In the first preferred embodiment of the present invention, at the second or third wiring pattern portion, the signal wiring pattern is electrically connected to the output end of the second surface acoustic wave filter chip via the bump.
According to a second preferred embodiment of the present invention, a surface acoustic wave branching filter includes a first surface acoustic wave chip filter having a relatively low center frequency and a second surface acoustic wave chip filter having a relatively high center frequency which are joined using a plurality of bumps provided on the first and second surface acoustic wave filter chips to wiring patterns of a chip-mounting surface of a packaging member. The surface acoustic wave branching filter includes a first surface acoustic wave filter chip that includes a plurality of SAW resonators and that has a plurality of bumps on the lower surface, a second surface acoustic wave filter chip that includes a plurality of SAW resonators and that has a plurality of bumps on the lower surface, and a packaging member to which the first and second surface acoustic wave filter chips are joined using the plurality of bumps. The chip mounting surface of the packaging member has, at least, a signal wiring pattern that is connected to an output end of the second surface acoustic wave filter chip and a ground wiring pattern that is connected to a ground potential of a SAW resonator that is in closest proximity to the output end of the second surface acoustic wave filter chip. The chip mounting surface has a signal via hole electrode and a ground via hole electrode which are connected to the signal wiring pattern and the ground wiring pattern, respectively, and which penetrate at least one portion of the packaging member. Of the distances between via hole electrodes that are arranged in the packaging member and that are connected to different potentials, the distance between the signal via hole electrode and the ground via hole electrode is a minimum.
According to a third preferred embodiment of the present invention, a surface acoustic wave branching filter includes a first surface acoustic wave filter chip having a relatively low center frequency and a second surface acoustic wave filter chip having a relatively high center frequency which are joined using a plurality of bumps provided on the first and second surface acoustic wave filter chips to wiring patterns of a chip-mounting surface of a packaging member. The surface acoustic wave branching filter includes a first surface acoustic wave filter chip that includes a plurality of SAW resonators and that has a plurality of bumps on the lower surface, a second surface acoustic wave filter chip that includes a plurality of SAW resonators and that has a plurality of bumps on the lower surface, and a packaging member to which the first and second surface acoustic wave filter chips are joined using the plurality of bumps. The chip mounting surface of the packaging member has, at least, a signal wiring pattern that is connected to an output end of the second surface acoustic wave filter chip and a ground wiring pattern that is connected to a ground potential of a SAW resonator that is in closest proximity to the output end of the second surface acoustic wave filter chip. A structure for canceling out magnetic flux is provided. When magnetic flux produced by an electrical signal flowing through the first surface acoustic wave filter chip flows in a region in which the signal wiring pattern and the ground wiring pattern are provided, the structure cancels out the magnetic flux.
In the third preferred embodiment of the present invention, in the structure for canceling out the magnetic flux, first and second via hole electrodes are arranged to penetrate at least one portion of the packaging member and are connected to the ground wiring pattern. The first and second via hole electrodes are distributed at two opposite sides of an imaginary line that connects a first bump and a second bump of a plurality of bumps that join the second surface acoustic wave filter chip to wiring patterns of the packaging member. The first bump is connected to the output end of the second surface acoustic wave filter chip and the second bump is connected to the ground potential of the SAW resonator that is in closest proximity to the output end.
In the third preferred embodiment of the present invention, in the structure for canceling out the magnetic flux, first and second via hole electrodes are arranged to penetrate a layer of at least one portion of the packaging member and are connected to the ground wiring pattern. The first and second via hole electrodes are distributed at two opposite sides of a line that connects a first bump and the center of a plurality of second bumps. The first bump is connected to the output end of the second surface acoustic wave filter chip and the second bumps is connected to the ground-side potential of the SAW resonator that is in closest proximity to the output end of the second surface acoustic wave filter chip.
In the third preferred embodiment of the present invention, the angle that is formed by a line connecting the first via hole electrode and the second bump and a line connecting the second bump and the second via hole electrode is about 90xc2x0 or more.
In the third preferred embodiment of the present invention, the angle that is formed by a line connecting the first via hole electrode and the center of the plurality of second bumps and a line connecting the center of the plurality of second bumps and the second via hole electrode is about 90xc2x0 or more.
In the third preferred embodiment of the present invention, a plurality of via hole electrodes including the first and second via hole electrodes is provided in the packaging member. At least one of the plurality of via hole electrodes is arranged in a region in which the second surface acoustic wave filter chip is mounted. The other via hole electrodes are arranged in a region outside the region in which the second surface acoustic wave filter chip is mounted.
In the surface acoustic wave device according to the first to third preferred embodiments of the present invention, the first and second surface acoustic wave filter chips may be configured as separated chips. In the present invention, however, the first and second surface acoustic wave filter chips may be integrated and configured as one: chip.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.